I have several videos on my PC that I would like to shorten. For instance I have a 30 sec video where I want to have the section from sec 15 to 20 (a 5sec video). To cut this, I use avconv.

avconv -i input.mp4 -ss 15 -acodec copy -vcodec copy -t 5 output.mp4

This command works pretty well. I have many videos I want to cut the same way. This is why I created a textfile containing the information: input-name, start of cut, length of cut, output-name. Those are written into in.txt that looks like this: